Merge #1224

1224: Update the blend API to upstream r=kvark a=kvark

**Connections**
Matches gpuweb/gpuweb#1134

**Description**
Makes blending state ON/OFF explicit.

**Testing**
Simple enough!

Co-authored-by: Dzmitry Malyshau <kvarkus@gmail.com>

wgpu-core/src/conv.rs

@@ -179,19 +179,13 @@ pub fn map_primitive_topology(primitive_topology: wgt::PrimitiveTopology) -> hal
 
 pub fn map_color_target_state(desc: &wgt::ColorTargetState) -> hal::pso::ColorBlendDesc {
     let color_mask = desc.write_mask;
-    let blend_state = if desc.color_blend != wgt::BlendState::REPLACE
-        || desc.alpha_blend != wgt::BlendState::REPLACE
-    {
-        Some(hal::pso::BlendState {
-            color: map_blend_state(&desc.color_blend),
-            alpha: map_blend_state(&desc.alpha_blend),
-        })
-    } else {
-        None
-    };
+    let blend = desc.blend.as_ref().map(|bs| hal::pso::BlendState {
+        color: map_blend_component(&bs.color),
+        alpha: map_blend_component(&bs.alpha),
+    });
     hal::pso::ColorBlendDesc {
         mask: map_color_write_flags(color_mask),
-        blend: blend_state,
+        blend,
     }
 }
 
@@ -215,21 +209,21 @@ fn map_color_write_flags(flags: wgt::ColorWrite) -> hal::pso::ColorMask {
     value
 }
 
-fn map_blend_state(blend_desc: &wgt::BlendState) -> hal::pso::BlendOp {
+fn map_blend_component(component: &wgt::BlendComponent) -> hal::pso::BlendOp {
     use hal::pso::BlendOp as H;
     use wgt::BlendOperation as Bo;
-    match blend_desc.operation {
+    match component.operation {
         Bo::Add => H::Add {
-            src: map_blend_factor(blend_desc.src_factor),
-            dst: map_blend_factor(blend_desc.dst_factor),
+            src: map_blend_factor(component.src_factor),
+            dst: map_blend_factor(component.dst_factor),
         },
         Bo::Subtract => H::Sub {
-            src: map_blend_factor(blend_desc.src_factor),
-            dst: map_blend_factor(blend_desc.dst_factor),
+            src: map_blend_factor(component.src_factor),
+            dst: map_blend_factor(component.dst_factor),
         },
         Bo::ReverseSubtract => H::RevSub {
-            src: map_blend_factor(blend_desc.src_factor),
-            dst: map_blend_factor(blend_desc.dst_factor),
+            src: map_blend_factor(component.src_factor),
+            dst: map_blend_factor(component.dst_factor),
         },
         Bo::Min => H::Min,
         Bo::Max => H::Max,

wgpu-core/src/device/mod.rs

@@ -2386,8 +2386,10 @@ impl<B: GfxBackend> Device<B> {
 
         let mut flags = pipeline::PipelineFlags::empty();
         for state in color_states.iter() {
-            if state.color_blend.uses_color() | state.alpha_blend.uses_color() {
-                flags |= pipeline::PipelineFlags::BLEND_COLOR;
+            if let Some(ref bs) = state.blend {
+                if bs.color.uses_color() | bs.alpha.uses_color() {
+                    flags |= pipeline::PipelineFlags::BLEND_COLOR;
+                }
             }
         }
         if let Some(ds) = depth_stencil_state.as_ref() {

wgpu-types/src/lib.rs

@@ -690,14 +690,12 @@ impl Default for BlendOperation {
     }
 }
 
-/// Describes the blend state of a pipeline.
-///
-/// Alpha blending is very complicated: see the OpenGL or Vulkan spec for more information.
+/// Describes the blend component of a pipeline.
 #[repr(C)]
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 #[cfg_attr(feature = "trace", derive(Serialize))]
 #[cfg_attr(feature = "replay", derive(Deserialize))]
-pub struct BlendState {
+pub struct BlendComponent {
     /// Multiplier for the source, which is produced by the fragment shader.
     pub src_factor: BlendFactor,
     /// Multiplier for the destination, which is stored in the target.
@@ -707,9 +705,9 @@ pub struct BlendState {
     pub operation: BlendOperation,
 }
 
-impl BlendState {
+impl BlendComponent {
     /// Default blending state that replaces destination with the source.
-    pub const REPLACE: Self = BlendState {
+    pub const REPLACE: Self = BlendComponent {
         src_factor: BlendFactor::One,
         dst_factor: BlendFactor::Zero,
         operation: BlendOperation::Add,
@@ -728,12 +726,26 @@ impl BlendState {
     }
 }
 
-impl Default for BlendState {
+impl Default for BlendComponent {
     fn default() -> Self {
         Self::REPLACE
     }
 }
 
+/// Describe the blend state of a render pipeline.
+///
+/// See the OpenGL or Vulkan spec for more information.
+#[repr(C)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
+#[cfg_attr(feature = "trace", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub struct BlendState {
+    /// Color equation.
+    pub color: BlendComponent,
+    /// Alpha equation.
+    pub alpha: BlendComponent,
+}
+
 /// Describes the color state of a render pipeline.
 #[repr(C)]
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
@@ -743,12 +755,9 @@ pub struct ColorTargetState {
     /// The [`TextureFormat`] of the image that this pipeline will render to. Must match the the format
     /// of the corresponding color attachment in [`CommandEncoder::begin_render_pass`].
     pub format: TextureFormat,
-    /// The alpha blending that is used for this pipeline.
-    #[cfg_attr(any(feature = "trace", feature = "replay"), serde(default))]
-    pub alpha_blend: BlendState,
-    /// The color blending that is used for this pipeline.
+    /// The blending that is used for this pipeline.
     #[cfg_attr(any(feature = "trace", feature = "replay"), serde(default))]
-    pub color_blend: BlendState,
+    pub blend: Option<BlendState>,
     /// Mask which enables/disables writes to different color/alpha channel.
     #[cfg_attr(any(feature = "trace", feature = "replay"), serde(default))]
     pub write_mask: ColorWrite,
@@ -758,8 +767,7 @@ impl From<TextureFormat> for ColorTargetState {
     fn from(format: TextureFormat) -> Self {
         Self {
             format,
-            alpha_blend: BlendState::REPLACE,
-            color_blend: BlendState::REPLACE,
+            blend: None,
             write_mask: ColorWrite::ALL,
         }
     }